How does political censorship work in liberal societies? When my film, 'Year Zero: the Silent Death of Cambodia', was banned in the United States in 1980, the broadcaster PBS cut all contact. Negotiations were ended abruptly; phone calls were not returned. Something had happened. But what? 'Year Zero' had already alerted much of the world to the horrors of Pol Pot, but it also investigated the critical role of the Nixon administration in the tyrant’s rise to power and the devastation of Cambodia.

Six months later, a PBS official told me, “This wasn’t censorship. We’re into difficult political days in Washington. Your film would have given us problems with the Reagan administration. Sorry.”

In Britain, the long war in Northern Ireland spawned a similar, deniable censorship. The journalist Liz Curtis compiled a list of more than 50 television films in Britain that were never shown or indefinitely delayed. The word “ban” was rarely used, and those responsible would invariably insist they believed in free speech.

The Lannan Foundation in Santa Fe, New Mexico, believes in free speech. The foundation’s website says it is “dedicated to cultural freedom, diversity and creativity”. Authors, film-makers, poets make their way to a sanctum of liberalism bankrolled by the billionaire Patrick Lannan in the tradition of Rockefeller and Ford.

Lannan also awards “grants” to America’s liberal media, such as Free Speech TV, the Foundation for National Progress (publisher of the magazine Mother Jones), the Nation Institute and the TV and radio programme Democracy Now! In Britain, Lannan has been a supporter of the Martha Gellhorn Prize for Journalism, of which I am one of the judges. In 2008, Patrick Lannan personally supported the presidential campaign of Barack Obama. According to the Santa Fe New Mexican, he is “devoted” to Obama.

On 15 June, I was due in Santa Fe, having been invited to share a platform with the distinguished American journalist David Barsamian. The foundation was also to host the US premiere of my new film, 'The War You Don’t See', which investigates the false image-making of war-makers, especially Obama.

I was about to leave for Santa Fe when I received an email from the Lannan official organising my visit. The tone was incredulous. “Something has come up,” she wrote. Patrick Lannan had called her and ordered all my events to be cancelled. “I have no idea what this is all about,” she wrote.

Baffled, I asked that the premiere of my film be allowed to go ahead as the US distribution largely depended on it. She repeated that “all” my events were cancelled, “and this includes the screening of your film”. On the Lannan website “cancelled” appeared across a picture of me. There was no explanation. None of my phone calls were returned, nor subsequent emails answered. A Kafka world of not-knowing descended.

The silence lasted a week until, under pressure from local media, the Foundation put out a brief statement that too few tickets had been sold to make my visit “viable” and that “the Foundation regrets that the reason for the cancellation was not explained to Mr. Pilger or to the public at the time the decision was made”. Doubts were cast by a robust editorial in the Santa Fe New Mexican. The paper, which has long played a prominent role in promoting Lannan events, disclosed that my visit had been cancelled before the main advertising and previews were published. A full-page interview with me had to be hurriedly pulled. “Pilger and Barsamian could have expected closer to a packed 820-seat Lensic [arts centre].”

The manager of The Screen, the Santa Fe cinema that had been rented for the premiere, was called late at night and told to kill all his online promotion for my film, but took it upon himself to re-schedule the film for 23 June. It was a sell-out, with many people turned away. The idea that there was no public interest was demonstrably not true.

Theories? There are many, but nothing is proven. For me, it is all reminiscent of the long shadows cast during the Cold War. “Something is going to surface,” said Barsamian. “They can’t keep the lid on this.”

My talk on 15 June was to have been about the collusion of American liberalism in a permanent state of war and the demise of cherished freedoms, such as the right to call government to account. In the United States, as in Britain, serious dissent - free speech - has been substantially criminalised. Obama, the black liberal, the PC exemplar, the marketing dream is as much a warmonger as George W. Bush. His score is six wars. Never in US history has a president prosecuted as many whistle-blowers; yet this truth-telling, this exercise of true citizenship, is at the heart of America’s constitutional first amendment. Obama’s greatest achievement is having seduced, co-opted and silenced much of liberal opinion in the United States, including the anti-war movement.

The reaction to the Lannan ban has been illuminating. The brave, like the great whistleblower Daniel Ellsberg, were appalled and said so. Similarly, many ordinary Americans called into radio stations and have written to me, recognising a symptom of far greater suppression. But some exalted liberal voices have been affronted that I dared whisper the word, censorship, about such a beacon of “cultural freedom”. The embarrassment of those who wish to point both ways is palpable. Others have pulled down the shutters and said nothing. Given their patron’s ruthless show of power, it is understandable. For them, the Russian dissident poet Yevgeny Yevtushenko once wrote, “When truth is replaced by silence, the silence is a lie.”